1. Field of the Invention
This invention relates to a hand-held power working machine, and in particular to a power transmission device for a working member and to the clipper blades (saw blades), which are designed to be disposed at the front portion of a power working machine such as a hedge trimmer.
2. The Prior Art
A hand-held power working machine, such as a hedge trimmer, is generally constituted by a prime mover case housing a prime mover, such as an internal combustion engine, a mount base portion supporting a transmission case housing a power transmission device, such as gears, to be actuated by the prime mover, a working portion comprising clipper blades to be actuated via the aforementioned power transmission device by the prime mover, and a handling portion attached to the prime mover case, the transmission case or the mount base portion. The handling portion is constituted, for the convenience of manipulation thereof, by a front handle portion and a rear handle portion. For the purpose of protecting an operator's hand gripping the front handle portion from accidents, a hand protector is attached to a portion in front of the front handle. The working portion comprising the clipper blades, etc. is disposed below the hand protector.
According to another type of conventional hand-held power working machine provided with a working portion comprising clipper blades, a prime mover, such as an internal combustion engine, is attached to one end portion of a long manipulating rod, and the working portion (comprising the clipper blades) is mounted, together with a transmission case, on the other end portion of the long manipulating rod. The rotating power of the prime mover is transmitted via a transmission shaft passed through the manipulating rod to the transmission case. Then, through a transmission device housed in the transmission case, the rotating power is further transmitted to the clipper blades of the working portion, thereby allowing the clipper blades to be driven reciprocatively so as to perform the cutting of lawns and other vegetation. (See, for example, Japanese Utility Model Publication H/6-905.)
FIG. 4 shows a cross-sectional view of a transmission case 50 and a working portion 60 comprising clipper blades 61 and 62 of the aforementioned hand-held power working machine. FIG. 5 shows the clipper blades 61 and 62, and a reciprocating movement-guiding arm 65 (66) for guiding the reciprocating movement of the clipper blades 61 and 62. As shown in FIG. 4, a main drive shaft 51, to be driven by the power of the prime mover (not shown), is rotatably supported in the transmission case 50. A driving rotor 52 provided with a pair of upper and lower eccentric circular cams 52a and 52b differing in phase from each other is drivably attached to the main shaft 51.
The working portion 60 is constituted by a pair of clipper blades 61 and 62 which are superimposed one upon the other. The clipper blades 61 and 62 are respectively provided not only with a plurality of cutting edges 61c and 62c formed at predetermined intervals on both sides of each blade (see FIG. 5), but also with a plurality of guiding slots 61a and 62a which are formed at predetermined intervals along the center line and in the longitudinal direction of each of the clipper blades 61 and 62.
On the upper surface of the upper clipper blade 61, there is disposed an upper blade-supporting plate 64 which is supported or cantilevered by the transmission case 50 by means of securing bolts 68 and locknuts 69. There is also disposed, on the bottom surface of the lower clipper blade 62, a lower blade-supporting plate 67, which is secured by a plurality of guiding screws 70 which are introduced from the bottom side of the lower blade-supporting plate 67 into the guiding slots 61a and 62a so as to allow the tip end portions thereof to protrude from the upper blade-supporting plate 64 and to be clamped by locknuts 71. The pair of the upper and lower clipper blades 61 and 62 are disposed in such a manner that, even in the aforementioned secured condition, they are capable of reciprocatively moving in the longitudinal direction thereof as guided by the combination of the guiding screws 70 within the guiding slots 61a and 62a. Guide collars 71a of appropriate height are positioned around the screws 70 to space the upper and lower plates 64 and 67 apart by the necessary distance.
As shown in FIG. 5, the reciprocating movement-guiding arms 65 and 66 are not only provided at the proximal end portion thereof with elliptical openings 65a and 66a, respectively, the minor axis of which is almost the same as that of the eccentric circular cams 52a and 52b, but are also provided at the distal end portion thereof with coupling members 65b and 66b each having a circular head.
The proximal end portions of the clipper blades 61 and 62 facing the aforementioned reciprocating movement-guiding arms 65 and 66 are provided with cutout engaging portions 61b and 62b, each having a shape conforming with the shape of the circular coupling members 65b and 66b. Namely, the cutout engaging portions 61b and 62b are adapted to be engaged with the coupling members 65b and 66b, while the elliptical openings 65a and 66a of the reciprocating movement-guiding arms 65 and 66 are adapted to be engaged with the eccentric circular cams 52a and 52b.
The transmission case 50, constructed as explained above, and the working portion 60, comprising the clipper blades 61 and 62, are interconnected in such a manner that when the main shaft 51 is rotated, thereby to rotate the driving rotor 52, the pair of upper and lower eccentric circular cams 52a and 52b (differing in phase from each other) are caused to rotate, thereby causing the clipper blades 61 and 62 to reciprocate, guided by the reciprocating movement-guiding arms 65 and 66, in opposite directions to each other with a phase shift of 180 degrees, thus making it possible to carry out the cutting of vegetation and the like.
According to the conventional hand-held power working machine, the reciprocating movement-guiding arms 65 and 66 are designed to be separated from the clipper blades 61 and 62 through disengagement of the circular coupling members 65b and 66b from the cutout engaging portions 61b and 62b. Accordingly, when it is desired to replace or sharpen the clipper blades 61 and 62, the clipper blades 61 and 62 can be separated from the reciprocating movement-guiding arms 65 and 66 by first unfastening and removing the locknuts 71 from the guiding male screws 70 and then dismounting the lower blade-supporting plate 67 from the upper blade-supporting plate 64.
However, since the reciprocating movement-guiding arms 65 and 66 are provided at the proximal end portions thereof with the elliptical openings 65a and 66a, respectively, to allow them to be reciprocatively driven by the driving rotor 52 (through the pair of upper and lower eccentric circular cams 52a and 52b), the reciprocating movement-guiding arms 65 and 66 are required to have a wide width in the direction perpendicular to the direction of reciprocation. Accordingly, a raw material plate of relatively large width is required for the manufacture of the reciprocating movement-guiding arms 65 and 66. At the same time, to ensure a sufficient structural strength in the region where the elliptical openings 65a and 66a are formed, the material plate must be of relatively large thickness or, alternatively, the ring portion surrounding the elliptical openings 65a and 66a must be enlarged in width. This design also involves a troublesome working during manufacture.
Further, since the reciprocating movement-guiding arms 65 and 66 are integrated with the clipper blades 61 and 62 through the engagement between the circular head coupling members 65b and 66b and the cutout engaging portions 61b and 62b and, at the same time, are reciprocatively moved while maintaining such integrated condition, a phenomenon of scoop-out tends to occur due to flexing stress in the engagement portions between the coupling members 65b and 66b and the cutout engaging portions 61b and 62b, thereby giving rise to rattling at the engagement portions therebetween.
Furthermore, the so-called integrated type clipper blades (where the reciprocating movement-guiding arms and the clipper blades are pivotally coupled with each other via a pin and which is widely employed in other types of conventional hand-held power working machine) cannot be used in the aforementioned type of hand-held power working machine where the reciprocating movement-guiding arms 65 and 66 are integrated with the clipper blades 61 and 62 through the above-described engagement. Namely, there is an inconvenience in that the clipper blades to be employed in the aforementioned type of hand-held power working machine are not interchangeable with other types of clipper blades.